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What are coolants
A coolant is a substance, typically liquid or gas used to reduce or regulate the temperature of a system. An ideal coolant with high thermal capacity and low viscosity is low-cost, non-toxic, chemically inert and neither causes nor promotes corrosion of the cooling system. Some applications also require the coolant to be an electrical insulator.
Coolant is a unique heat transfer fluid substance used to regulate the temperature of engines and machines. It is also known as antifreeze, mostly with ethylene glycol or propylene as the main ingredient. Coolant is generally 50-50 of antifreeze and water, which provides the best heat transfer. It protects the engine from freezing and prevents corrosion of metal parts due to corrosion inhibitors. They are of different types and usually appear in different colors such as green, blue, etc.
However, in this article, we are particular about Marine diesel engine coolant and antifreeze, used explicitly for engines operating on the water.
The different types of cooling for Marine engines
In the marine industry, diesel-powered generators rely on multiple cooling systems. Each has its proper applications in the field for different circumstances. Before you choose a particular cooling system for your backup generator, make sure it’s powerful enough to handle the amount of heat the engine will produce. Let’s look closely at a few different marine generator cooling systems.
Radiator Cooling
One prevalent type of cooling system is radiator cooling. A water jacket built around the generator allows coolant liquid to flow close to the machine, picking up heat. The coolant then flows to the radiator, where the heat is removed and returned to the engine to repeat the cycle. This widespread setup is likely what your new marine generator will use.
Pro Tip: Coolant liquid in generators is usually water-based. Talk to an expert to see if your particular generator needs a different type of coolant.
Keel Cooling
The Keel cooling type is specifically designed for fully submerged generators and operates similarly to radiator cooling with an exciting twist. Coolant flows through a water jacket to absorb heat from the generator. However, instead of entering a radiator to get rid of the heat, the coolant is directed through pipes exposed to cooler underwater temperatures. This system depends on the surrounding water to keep heat levels down.
Heat Exchange
Both major cooling systems rely on the principle of heat exchange. Heat naturally flows to more excellent areas whenever it can, and coolant systems take advantage of this fact to deflect heat elsewhere. The engine passes its heat to the lower-temperature coolant liquid, and the fluid then passes that heat to the even cooler air or water outside the generator. Either way, your generator’s temperature stays at a manageable level.
Engine cooling systems properly explained
The process starts by drawing water into the engine through a seacock fitting and pumping it through the engine’s water jacket and ports through a mechanical water pump. In a raw water system, the water is drawn up through the seacock by the water pump. The water flows through the engine and directly out the exhaust. This cooler water absorbs heat from the engine to help keep it cool. Most newer marine engines use an enclosed cooling system. This means a small tank on the top of the engine uses a combination of fresh water and coolant. In this system, fresh water absorbs the engine’s heat. This freshwater is circulated through the engine and a heat exchanger. Raw water is still drawn up through the seacock but only flows through the heat exchanger jacket. This cooler plain water absorbs the heat from the freshwater through the heat exchanger jacket and is pumped out the exhaust.
The advantages of the enclosed system over the raw water system are extreme, primarily if you operate in salt water. Salt water builds up a corrosive scale when the engine uses above 140°. This scale builds up inside the engine’s water jacket and ports in the raw water system. The engine overheats when the scaling builds to the point that water flow is restricted. At this point, you are probably looking at replacing the engine.
In the enclosed system, the water that flows through the engine’s water jacket and ports is the fresh water and coolant. The only part the raw water flows through is the heat exchanger. The same scaling occurs, however. When water flow is restricted and the engine begins to overheat, you may be able to “acid boil” the scale-out of the heat exchanger and continue to use it. The worse case is that you would have to replace the heat exchanger. This would be much less expensive than replacing the engine.
Other components of the cooling system, whether raw water or enclosed, are the seacock, sea filter, hoses and clamps, belts, and water pump impeller.
The seacock is a through-hull device that allows water to enter the hull from the outside. This device has a handle that will enable you to shut off the water flow if you have a problem, such as a loose hose clamp or cracked hose. You should test the seacock shut-offs monthly to make sure they are operable. As a backup safety measure, you should have a soft, tapered, wooden plug (called a bung) of the size of the seacock tied to the seacock. If a hose parts and you can’t operate the shut-off, you can put the bung in the seacock to stop the water flow.
The following inline part of the engine cooling system is the sea strainer. This is a device through which the raw water flows and filters out debris, sand, leaves, etc., before it gets to the engine. This device works much like a swimming pool skimmer. There are several strainers, but all have a removable filter or screen that should be checked, cleaned, or replaced regularly.
Hoses, clamps, and belts are vital to the cooling system and should also be checked periodically. Every time you check the oil before each start-up, you should visually inspect hoses, clamps, and belts for wear. All hoses that are below the waterline should be double clamped. This will help prevent water from entering the bilge should one of the clamps fail. If you find a corroded clamp, a pinched or cracked hose, or a belt, we should replace them immediately. Be sure to replace the hoses with the same size, diameter, length, and temperature requirements that the manufacturer suggests.
The raw water pump, driven by a belt on the engine, contains an impeller that makes the pump operate. It is usually relatively easy to access the impeller to inspect or replace it.
A commercial coolant (antifreeze) should be added to the enclosed system. This will prevent the fresh water from freezing and damaging the engine in cold climates and help avoid corrosion in the freshwater system. Usually, you would use the coolant and fresh water in a 50/50 mixture. In colder climates, you may want to increase the coolant percentage.
In summary, the direct, raw water system circulates water through the engine water jacket, which flows through the block, head, manifold, etc. This water absorbs the heat from the engine and is exhausted overboard.
The enclosed system circulates fresh water and coolant through the engine water jacket and a heat exchanger. This freshwater absorbs the heat of the engine. The raw water is also pumped through the heat exchanger, where it absorbs some of the heat of the fresh water and is again exhausted overboard.
Managing Your Generator’s Temperature
Unchecked heat in a diesel generator can slow down functionality and cause long-term damage if ignored for long enough. Thankfully, the proper coolant system can prevent either from happening.
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